Re: [RFC PATCH] midx.c: clean up .rev file

Thanks for your attention.

* The `gettext()` and `fputs()` which calls in `die_errno(_())` are seem
highly unlikely async-signal-safety, this may cause problems in signal
handlers, I should remove it.
* This is thread-safe. The *.rev file will no longer be read/written after
creating the signal handler by `sigchain_push_common()`.
* On the other hand, the command: `git multi-pack-index write --bitmap` will
create an lockfile named `multi-pack-index.lock` and the signal handler
will not affect the execution of the same command or git-process.

The purpose of this patch is the same as what Teng Long said, to clean up the files generated by the process when the process exits abnormally.

Thanks.